FIG. 1 illustrates a Gore-Tex® breathable and waterproof fabric for outdoor clothing. The Gore-Tex® breathable and waterproof fabric includes an outer shell 11, an inner liner 12, and a triply structure interposed between the outer shell 11 and the inner liner 12. The triply structure includes a breathable and waterproof sponge-like porous membrane 13 sandwiched between two protection layers 14. The porous membrane 13 is made from a polymer, such as Teflon®, polyvinylidene fluoride (PVDF), and polyurethane, and is formed with pores in a known manner, such as that disclosed in U.S. Pat. Nos. 3,953,566 and 4,187,390. The pores formed in the porous membrane 13 have a pore diameter in the order of less than one micron in order to permit transpiration of water vapor therethrough and prevent water from passing therethrough. The porous membrane 13 has a thickness ranging from 50 microns to several hundreds of microns.
Referring to FIG. 2, U.S. Patent Application Publication No. 2004/0256310 discloses a method of making a highly breathable and waterproof fabric including a multilayered fabric sheet 21, a breathable and waterproof sponge-like porous membrane 22 (with a trademark NanoTex®) formed on the fabric sheet 21, and a hydrophilic layer 23 formed on the porous membrane 22. The method involves the steps of providing a solution of PVDF in a solvent, coating the solution on the fabric sheet 21 to form a film of the solution, and bringing a liquid material into contact with the film so as to leach the solvent from the solution of PVDF and to cause gelation of PVDF so as to form the porous membrane 22 on the fabric sheet 21. The porous membrane 22 has a pore size ranging from 100 nm to 10 μm, and preferably ranging from 100 nm to 1000 nm so as to obtain satisfactory waterproofness and breathability. In one example, the porous membrane 22 has a maximum pore size of about 0.3 μm in order to be waterproof under a 60 mph raindrop velocity. Moreover, the porous membrane has a breathability ranging from 4000 to 10000 g/m2/day. It is noted that FIG. 4 of the specification of U.S. Patent Application Publication No. 2004/0256310 shows a comparison between a structure of the porous membrane 22 (NanoTex®) and a structure of the porous membrane 13 (Gore-Tex®) of FIG. 1. Both of the structures show irregular and randomly distributed pores.
The costs of making the aforesaid porous membranes 13, 22 are high.